Blood vessel occlusions are commonly treated by mechanically enhancing blood flow in the affected vessels, such as by employing a stent. Stents act as scaffoldings, functioning to physically hold open and, if desired, to expand the wall of affected vessels. Typically stents are capable of being compressed, so that they can be inserted through small lumens via catheters, and then expanded to a larger diameter once they are at the desired location. Examples in the patent literature disclosing stents include U.S. Pat. No. 4,733,665 issued to Palmaz, U.S. Pat. No. 4,800,882 issued to Gianturco, and U.S. Pat. No. 4,886,062 issued to Wiktor.
FIG. 1 illustrates a conventional stent 10 formed from a plurality of struts 12. The plurality of struts 12 are radially expandable and interconnected by connecting elements 14 that are disposed between adjacent struts 12, leaving lateral openings or gaps 16 between adjacent struts 12. The struts 12 and the connecting elements 14 define a tubular stent body having an outer, tissue-contacting surface and an inner surface.
Stents are used not only for mechanical intervention but also as vehicles for providing biological therapy. Biological therapy can be achieved by medicating the stents. Medicated stents provide for the local administration of a therapeutic substance at the diseased site. Local delivery of a therapeutic substance is a preferred method of treatment because the substance is concentrated at a specific site and thus smaller total levels of medication can be administered in comparison to systemic dosages that often produce adverse or even toxic side effects for the patient.
One method of medicating a stent involves the use of a polymeric carrier coated onto the surface of the stent. A composition including a solvent, a polymer dissolved in the solvent, and a therapeutic substance dispersed in the blend is applied to the stent by immersing the stent in the composition or by spraying the composition onto the stent. The solvent is allowed to evaporate, leaving on the stent strut surfaces a coating of the polymer and the therapeutic substance impregnated in the polymer.
A shortcoming of the above-described method of medicating a stent is that both the inner surface and an outer surface of the stent are coated with the same therapeutic substance. Accordingly, the therapeutic substance will be dispensed locally by being absorbed by the vessel wall from the outer surface of the stent and will be dispensed downstream as blood carries the therapeutic substance from the inner surface. In some circumstances there may be a need of only having the outer surface of the stent coated with the therapeutic substance. Alternatively, there may be a need of coating the outer surface of the stent with a first type of a drug and the inner surface with a second type of a drug. For example, the stent's outer surface could be coated with an anti-inflamatory drug or anti-restenosis drug to treat inflammation or hyper-migration and proliferation of vascular smooth muscle cells, respectively. The stent's inner wall could be coating with an anti-coagulant to reduce platelet aggregation, clotting and thrombus formation.
Accordingly, a new stent mandrel fixture and method are needed to overcome this shortcoming.